Transportation in Plants

Matthew Gibson                 Joliet West High School
                               401 N. Larkin
                               Joliet IL 60435
                               (815) 727-6950

Objectives:

This lesson is designed for middle school and high school.  The objectives for 
this lesson are as follows:  1) Students will understand how the forces of 
adhesion and cohesion and the process of transpiration aid in the transportation
of water through the plant.  2) Students will recognize the form and function of
stomata.

Materials:

Glass tube (hollow; the smaller the diameter, the better)
Celery Stalks (with leaves; about 10 stalks for every 25 students) 
Microscopes, slides, and cover-slips
Food coloring
2 glass containers
Scalpel
Scotch tape
Clear nail polish
Leaves from plants

Strategy:

1) preparation: mix several drops of blue food coloring with water in the glass
container.  Place the celery stalks in the container 4 days prior to the date 
the class will be using the celery.  After mixing food coloring and water in the 
second container, insert the glass tube (the water should creep up the tube, but 
will not reach the top.)  Collect leaf samples from around the campus. 

2) the lesson: 
PART 1: Have the students observe the water in the tube.  Ask them why the water 
is creeping up the glass rod, apparently defying gravity.  After discussing how 
the forces of adhesion and cohesion are responsible for the ascending water, 
have them compare the celery and the glass tube in terms of how high the water 
ascended.  Students should notice that the water in the celery has risen to the 
tips of the leaves, while the water in the glass tube is much lower.  Then pose 
the following question: "Why did the water rise so high in the leaves but not in 
the glass tube?"  Following their responses, explain the 
Adhesion/cohesion/transpiration theory (include how the gradient of water 
potential moves water from cell to cell to cell to stomata.)  Have the students 
view a thin cross section of celery under the microscope to discover the 
location of the xylem cells which are stained blue. 

PART 2: Paint a small section of the underside of a leaf with clear nail polish. 
Let it dry completely.  When dry, peel the polish off the leaf by pressing 
scotch tape to it.  If done carefully, the polish should stay attached to the 
tape as you peel it away from the leaf.  Affix the tape to a slide and search 
for the imprint of stomata in the polish (practice this method ahead of time). 
Once the students can recognize stomata, have them compare how many stomata are 
located on the underside of the leaf versus the top of the leaf.  Relate their 
findings to solar radiation, transpiration, and the cuticle.  

Performance Assessment:

To assess the student's comprehension of the lesson the following quiz would be 
administered:
   1.  Explain in detail how the forces of adhesion and cohesion and the process 
       of transpiration aid in the transportation of water through the plant.
 
   2.  Predict what would happen to a plant if all of it's stomata became          
       plugged by a substance that prevented the passage of matter into and out 
       of the leaves.  Provide an explanation for your prediction.

This quiz would be worth 6 points.  The following rubric would be used for 
awarding points: Question #1 is worth 4 points with 1 point awarded for each of 
the explanations of adhesion, cohesion, and transpiration.  The final point would 
be awarded for an overall coherent answer.  Question #2 is worth 2 points, with 
1 point awarded for a reasonable prediction and 1 point for an accurate 
explanation.